1. Field of the Invention
The present invention relates to a feeding structure for a gyro rotor in a gyrocompass which includes a liquid tank containing a supporting liquid therein, a gyrosphere which floats in the liquid tank by means of a supporting liquid and whose central portion is rotatably supported by a center pin provided in an upper portion of the liquid tank, and a gyro rotor incorporated in the gyrosphere.
2. Description of the Related Art
The following publication is known as a document relating to the gyrocompass having a center pin.
“konpasu to jairo no riron to jissai (Theory and practice of compass and gyro)” published on Oct. 1, 1971 by Kaibundou Shuppan Kabushiki Kaisha; Authors: Torao Mozai and Minoru Kobayashi
FIG. 5 is a cross-sectional view illustrating a general configuration of a gyrocompass having a center pin. Reference numeral 1 denotes a computation and follow-up control unit which is a portion which controls the power supply of the apparatus and various arithmetic operations and is in charge of follow-up control for maintaining the relative angle between a gyrosphere and a liquid tank by detecting the position of the gyrosphere. The computation and follow-up control unit 1 mainly consists of a gear mechanism for follow-up and printed board circuits.
Reference numeral 2 denotes a vibration proofing mechanism for maintaining a liquid tank unit substantially horizontally by inclination like a pendulum and for absorbing the vibrations of a ship in the longitudinal and transverse directions of the ship when the ship has rocked.
Reference numeral 3 denotes a liquid tank unit which is suspended in the vibration proofing mechanism 2. In the liquid tank unit 3, a liquid tank 4 has a gyrosphere 5 and an electrolyte (supporting liquid) 6 incorporated therein. The gyrosphere 5 has a gyro rotor 7 incorporated therein, and floats in the liquid tank 4 by means of the supporting tank 6, and its central portion is rotatably supported by a center pin 8 provided in an upper portion of the liquid tank.
FIG. 6 is a perspective view illustrating a feeding structure for the gyrosphere 5. Two dish-shaped electrodes 9, which are disposed in close proximity to and in face-to-face relation to each other through the supporting liquid 6, are respectively formed at a lower portion of the liquid tank 4 and a lower portion of the gyrosphere 5. Electric power is fed from an external power supply 10 to the gyro rotor 7 incorporated in the gyrosphere 5 through the center pin 8 and the dish-shaped electrodes 9. It should be noted that the surface of the gyrosphere other than the electrode is insulated.
FIG. 7 is a cross-sectional view illustrating the details of the feeding structure through the center pin. The tip of the center pin 8 is tapered, and this tip and a jewel bearing 11 provided on the gyrosphere side form a pivot, which allows the gyrosphere 5 floating in the supporting liquid 6 to be supported rotatably vertically and horizontally. Meanwhile, a small amount of mercury 14 is filled in a gap between a tip metal portion 8a of the center pin and a pot-like metal portion 13 conducting with a terminal 12 on the gyrosphere side, thereby forming one feeding circuit from the center pin 8 to the gyrosphere 5. Reference numeral 15 denotes insulating oil such as Demnum (trade name; product of Daikin Industries, Ltd.) for insulating the mercury 14 and the supporting liquid 6, and numeral 16 denotes an O-ring for sealing the entry of the supporting liquid into the gyrosphere.
The gyro rotor 7 is connected to the one feeding circuit through the center pin 8 and the other feeding circuit for allowing an electric current to flow through the supporting liquid 6 by the dish-shaped electrodes 9 respectively formed at the lower portion of the liquid tank 4 and the lower portion of the gyrosphere 5 in face-to-face relation to each other, and the gyro rotor 7 rotates at high speed inside the gyrosphere.
FIG. 8 is a diagram explaining a deviation detecting mechanism in the follow-up control for causing the liquid tank 4 to follow up the gyration of the gyrosphere 5. A pair of (two) follow-up electrodes 17a and 17b are provided on an inner wall of the liquid tank 4 at positions opposing an equatorial portion of the gyrosphere 5 and spaced apart from each other by 180°. A belt-shaped electrode 18, which is slightly shorter than 180° (2° each at both ends), is formed at the equatorial portion of the gyrosphere 5, and a difference in resistance between supporting liquid resistors Ra and Rb between both ends 18a and 18b of the belt-shaped electrode 18 and the follow-up electrodes 17a and 17b is detected by a Wheatstone bridge.
The belt-shaped electrode 18 is connected to the dish-shaped electrode 9 at the lower portion of the gyrosphere and is set at the same potential, and is connected to one terminal of the external power supply 10 through the dish-shaped electrode 9. The gyro rotor 7 is connected between this dish-shaped electrode 9 and the tip metal 8a of the center pin 8, and electricity is fed thereto.
The follow-up electrodes 17a and 17b are connected to both ends of a primary winding of a transformer 19 for forming a Wheatstone bridge, and a midpoint of the primary winding is connected to one terminal of the external power supply 10 via a resistor 20 for current regulation. In a steady state, Ra=Rb, and the Wheatstone bridge is balanced and the induced voltage to a secondary winding of the transformer 19 is zero.
When the gyrosphere 5 gyrates in the direction of arrow P, and the relative angular relationship with the liquid tank 4 is offset about the vertical axis, Ra≠Rb, and a deviation (error voltage) in consequence of the imbalance of the Wheatstone bridge is induced in the secondary winding of the transformer 19, so that a deviation signal E is obtained through an amplifier 21. The amplitude of this deviation signal E represents a deviation angle, and the phase the gyrating direction.
The follow-up control unit 1 has the follow-up function whereby the gear mechanism is driven on the basis of this deviation signal E to simultaneously rotate the vibration proofing mechanism 2 and the liquid tank unit 3 in the direction of Q about the vertical axis, thereby correcting the relative angular relationship between the gyrosphere 5 and the liquid tank 4 such that the Wheatstone bridge becomes balanced.
The supporting liquid 6 is an electrolyte whose major agent is benzoic acid. Further, the specific gravity of the supporting liquid 6 has been adjusted by dynamite glycerin so that the gyrosphere 5 is always set in a floating state with respect to the ambient temperature.
The gyrocompass having the above-described conventional structure has the following problems.    (1) Mercury is used in a feeding route through the center pin, and it is desirable not to use mercury in the light of the protection of the global environment.    (2) If mercury is used in the electrolyte, ions are adsorbed on the center pin surface, the mercury surface, and the pot-like metal portion of the gyrosphere due to the electro-capillarity phenomena, and the intermolecular force of ions acts as a restraining force and hampers the “frictionless free rotation of the gyrosphere,” exerting an adverse effect on the accuracy. As a measure, this problem can be solved by interposing the insulating oil 15 such as Demnum (tetrafluoroethylene) or the like between the mercury 14 and the supporting liquid 6, as explained with reference to FIG. 7, but this insulating oil is not friendly to the global environment, either.